Wave reducer, industrial machine, drive system, and correction method

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2023-138717, filed on Aug. 29, 2023, the entire contents of which are incorporated herein by reference.

The present disclosure relates to wave reducers, industrial machines, drive systems, and correction methods.

There is a known reducer including a detection device having a plurality of strain gauges.

In this type of reducer, an angle sensor can be configured using a plurality of strain gauges. In that case, two sets of bridge circuits are configured by the plurality of strain gauges. The output values of the two sets of bridge circuits having a sinusoidal shape. The two sets of bridge circuits are arranged so as to have a phase difference of about ¼ cycle from each other. The angle sensor detects the rotation angle of a rotational motion input to the reducer based on the output values of the two sets of bridge circuits.

The amplitude of the output values of the bridge circuits is substantially constant. However, when a force acts from an input side of the reducer as in acceleration of a motor, or when an external force acts from an output side of the reducer, the amplitude of the output value of the bridge circuit slightly changes due to the thrust force applied to a cam of the reducer. Specifically, when a force acts from the input side of the reducer, the amplitude of the output value of the bridge circuit slightly decreases. When a force acts from the output side of the reducer, the amplitude of the output value of the bridge circuit slightly increases. Due to this, an error occurs in the detection value of the angle sensor.

An example embodiment of the present application provides a wave reducer including a cam including a non-circular outer surface, a flex gear flexurally deformable by rotation of the cam, an internal gear meshing with the flex gear, an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam, a thrust sensor located in the flex gear and having an output value that is variable in accordance with a thrust force applied to the cam, and a circuit electrically connected to the angle sensor and the thrust sensor. The circuit is operable to correct an output value of the angle sensor based on an output value of the thrust sensor.

Another example embodiment of the present application provides a drive system including a wave reducer and a circuit. The wave reducer includes a cam including a non-circular outer surface, a flex gear flexurally deformable by rotation of the cam, an internal gear meshing with the flex gear, an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam, and a thrust sensor located in the flex gear and having an output value that is variable in accordance with a thrust force applied to the cam, and the circuit is operable to correct an output value of the angle sensor based on an output value of the thrust sensor.

A further example embodiment of the present application provides a correction method of correcting an output value of an angle sensor in a wave reducer including a cam including a non-circular outer surface, a flex gear flexurally deformable by rotation of the cam, an internal gear meshing with the flex gear, the angle sensor located in the flex gear, the angle sensor having an output value that is variable in accordance with a rotation angle of the cam, and a thrust sensor located in the flex gear and having an output value that is variable in accordance with a thrust force applied to the cam, the correction method including correcting the output value of the angle sensor based on an output value of the thrust sensor.

Another example embodiment of the present application provides a wave reducer including a cam including a non-circular outer surface, a flex gear flexurally deformable by rotation of the cam, an internal gear meshing with the flex gear, an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam, and a circuit electrically connected to the angle sensor. The angle sensor includes two sets of bridge circuits including a plurality of strain gauges, output values of the two sets of bridge circuits have a phase difference of about ¼ cycle, and the circuit is operable to correct output values of the two sets of bridge circuits so as to cause a sum of squares of the output values of the two sets of bridge circuits to be equal or approximately equal to a constant value.

An additional example embodiment of the present application provides a drive system including a wave reducer and a circuit. The wave reducer includes a cam including a non-circular outer surface, a flex gear flexurally deformable by rotation of the cam, an internal gear meshing with the flex gear, and an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam, and the angle sensor includes two sets of bridge circuits including a plurality of strain gauges, output values of the two sets of bridge circuits have a phase difference of about ¼ cycle, and the circuit is operable to correct output values of the two sets of bridge circuits so as to cause a sum of squares of the output values of the two sets of bridge circuits to be equal or approximately equal to a constant value.

Yet another example embodiment of the present application provides a correction method of correcting an output value of an angle sensor in a wave reducer including a cam including a non-circular outer surface, a flex gear flexurally deformable by rotation of the cam, an internal gear meshing with the flex gear, and an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam. The angle sensor includes two sets of bridge circuits including a plurality of strain gauges, output values of the two sets of bridge circuits have a phase difference of about ¼ cycle, and the circuit is operable to correct output values of the two sets of bridge circuits so as to cause a sum of squares of the output values of the two sets of bridge circuits to be equal or approximately equal to a constant value.

The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.

Hereinafter, example embodiments of the present application will be described with reference to the drawings.

1 FIG. 1 FIG. 100 1 100 100 101 102 103 1 is a schematic view of an industrial machineincluding a wave reduceraccording to one example embodiment. The industrial machineis a so-called industrial robot that performs work such as conveyance, processing, and assembly of components in a manufacturing line of an industrial product, for example. As illustrated in, the industrial machineincludes a base frame, an arm, a motor, and the wave reducer.

102 101 103 1 101 102 103 103 1 102 103 102 101 The armis pivotally supported with respect to the base frame. The motorand the wave reducerare incorporated in a joint between the base frameand the arm. When the motoris supplied with a drive current, rotational motion is output from the motor. The wave reducerdecelerates and transmits, to the arm, the rotational motion output from the motor. Due to this, the armpivots with respect to the base frameat a speed after deceleration.

1 Subsequently, a detailed structure of the wave reducerwill be described.

9 1 9 1 9 1 Hereinafter, a direction parallel to a central axisof the wave reduceris called “axial”, a direction orthogonal to the central axisof the wave reduceris called “radial”, and a direction along an arc about the central axisof the wave reduceris called “circumferential”. Note, however, the “parallel” described above includes substantially parallel. The “orthogonal” described above also includes substantially orthogonal.

2 FIG. 3 FIG. 2 FIG. 3 FIG. 1 1 is a longitudinal cross-sectional view of the wave reduceraccording to one example embodiment.is a transverse cross-sectional view of the wave reducerviewed from A-A position in. To avoid complication of the drawings, hatching that indicates a cross section is not shown in.

1 103 1 10 20 30 40 2 3 FIGS.and The wave reduceris a device that decelerates the rotational motion at a first rotational speed output from the motorto a second rotational speed slower than the first rotational speed. As illustrated in, the wave reducerincludes an input shaft, an internal gear, a flex gear, and a wave generator.

10 10 103 10 9 10 9 10 1 10 103 The input shaftis a member that rotates at the first rotational speed before deceleration. The input shaftis connected to an output shaft of the motor. The input shaftextends in the axial direction along the central axis. The input shaftof the present example embodiment has a cylindrical shape about the central axis. The input shaftaxially penetrates the wave reducer. The input shaftmay be the same member as the output shaft of the motor.

20 30 20 10 20 102 20 32 20 31 30 The internal gearis a gear that meshes with the flex gear. The internal gearrotates at the second rotational speed lower than the first rotational speed along with the rotation of the input shaft. The internal gearis fixed to the arm. The internal gearis disposed radially outside external teethdescribed later. Rigidity of the internal gearis sufficiently higher than rigidity of a bodydescribed later of the flex gear.

20 9 20 21 21 20 21 20 The internal gearhas a circular shape centered on the central axis. The internal gearhas a plurality of internal teeth. The plurality of internal teethprotrude radially inward from an inner peripheral surface of the internal gear. The plurality of internal teethare arrayed at a constant pitch in the circumferential direction on the inner peripheral surface of the internal gear.

30 41 30 101 30 31 32 33 34 2 3 FIGS.and The flex gearis a gear flexurally deformed due to rotation of a camdescribed later. The flex gearis fixed to the base frame. As illustrated in, the flex gearincludes a body, a plurality of external teeth, a diaphragm, and a thick part.

31 9 31 33 31 33 31 40 20 31 The bodyis a tubular part centered on the central axis. An axial one end of the bodyis connected to the diaphragm. The bodyextends from a radial inner end part of the diaphragmtoward the axial other side. The end part on the axial other side of the bodyis positioned radially outside the wave generatorand radially inside the internal gear. Since the bodyhas flexibility, it can be flexurally deformed in the radial direction.

32 31 32 31 32 32 21 21 20 32 30 The plurality of external teethprotrude radially outward from the radial outer surface of the body. The plurality of external teethare arranged on the radial outer surface of the axial other end of the body. The plurality of external teethare arrayed at a constant pitch in the circumferential direction. Some of the plurality of external teethand some the plurality of internal teethdescribed above mesh with each other. The number of the internal teethof the internal gearis slightly different from the number of the external teethof the flex gear.

33 9 9 33 9 33 31 33 9 33 The diaphragmsurrounds the central axisand expands in a direction intersecting the central axis. The diaphragmpreferably extends along a plane orthogonal to the central axis. The diaphragmexpands radially outward from an axial one end of the body. The diaphragmhas an annular shape surrounding the central axis. Since the diaphragmis thin, it can be slightly flexurally deformed.

34 33 34 33 34 101 The thick partis a circular part positioned radially outside the diaphragm. The axial thickness of the thick partis larger than the axial thickness of the diaphragm. The thick partis fixed to the base framedirectly or via another member.

40 30 40 32 40 41 42 10 41 41 10 41 10 41 30 41 41 9 The wave generatoris a mechanism that generates periodic flexural deformation in the flex gear. The wave generatoris disposed radially inside the external teeth. The wave generatorincludes the camand a flexible bearing. In the present example embodiment, the input shaftand the camare formed of a single component. However, the cammay be a separate component from the input shaft. In that case, the cammay be fixed to the input shaft. The camis a component that gives the flex geardisplacement with a period of 180°. The camhas a non-circular outer surface. The camof the present example embodiment has an elliptical outer surface about the central axis.

42 42 41 31 30 The flexible bearingis a flexurally deformable bearing. The flexible bearingis disposed between the radial outer surface of the camand the radial inner surface of the bodyof the flex gear.

42 41 42 31 31 41 32 30 21 20 32 21 An inner ring of the flexible bearingcomes into contact with the radial outer surface of the cam. An outer ring of the flexible bearingcomes into contact with the radial inner surface of the body. Therefore, the bodyis deformed into an elliptical shape along the radial outer surface of the cam. As a result, the external teethof the flex gearand the internal teethof the internal gearmesh with each other at two locations corresponding to both ends of the major axis of the ellipse. At other positions in the circumferential direction, the external teethand the internal teethdo not mesh with each other.

103 10 41 9 30 32 21 21 20 32 30 32 21 41 20 9 30 When the motoris driven, together with the input shaft, the camrotates at the first rotational speed about the central axis. Due to this, the major axis of the ellipse of the flex gearalso rotates at the first rotational speed. Then, the meshing position between the external teethand the internal teethalso changes at the first rotational speed in the circumferential direction. As described above, the number of the internal teethof the internal gearis slightly different from the number of the external teethof the flex gear. Due to this difference in the number of teeth, the meshing position between the external teethand the internal teethslightly changes in the circumferential direction every rotation of the cam. As a result, the internal gearrotates about the central axiswith respect to the flex gearat the second rotational speed slower than the first rotational speed.

1 50 50 51 51 33 2 FIG. The wave reducerincludes a sensor. As illustrated in, the sensorincludes a sensor substrate. The sensor substrateis fixed to the surface of the diaphragm.

4 FIG. 5 FIG. 4 FIG. 30 51 51 51 511 512 is a partial longitudinal cross-sectional view of the flex gearnear the sensor substrate.is a plan view of the sensor substrate. As illustrated in, the sensor substrateincludes an insulation layerand a conductor layer.

511 511 9 511 9 511 511 33 512 511 512 512 The insulation layeris flexibly deformable. The insulation layerexpands in a direction intersecting the central axis. The insulation layerhas a circular shape about the central axis. The insulation layeris made of an insulator resin or an inorganic insulating material. The insulation layeris disposed on the surface of the diaphragm. The conductor layeris formed on the surface of the insulation layer. As a material of the conductor layer, a conductor metal is used. As a material of the conductor layer, for example, a copper alloy, a chromium alloy, or copper is used.

512 60 70 80 60 70 80 50 52 52 60 70 80 2 FIG. The conductor layerincludes a torque sensor, an angle sensor, and a thrust sensor. Each of the torque sensor, the angle sensor, and the thrust sensorincludes a strain gauge. As illustrated in, the sensorincludes a circuit. The circuitis electrically connected to the torque sensor, the angle sensor, and the thrust sensor.

60 33 30 60 30 60 61 62 62 61 5 FIG. The torque sensoris a sensor for detecting torque applied to the diaphragmof the flex gear. That is, the torque sensoris a sensor having an output value that is variable in accordance with the torque applied to the flex gear. As illustrated in, the torque sensorof the present example embodiment includes a first torque sensorand a second torque sensor. The second torque sensoris disposed radially outward relative to the first torque sensor.

61 9 9 9 The first torque sensorincludes four strain gauges Ra, Rb, Rc, and Rd. Among the four strain gauges Ra, Rb, Rc, and Rd, the two strain gauges Ra and Rb are arranged at intervals in the circumferential direction. The two strain gauges Ra and Rb are each provided in a semicircular arc shape in a range of about 180° centered on the central axis. The radial distance from the central axisto the strain gauge Ra and the radial distance from the central axisto the strain gauge Rb are substantially the same.

9 9 9 Among the four strain gauges Ra, Rb, Rc, and Rd, the other two strain gauges Rc and Rd are arranged radially outside relative to the two strain gauges Ra and Rb. The two strain gauges Rc and Rd are arranged at intervals in the circumferential direction. The two strain gauges Rc and Rd are each provided in a semicircular arc shape in a range of about 180° centered on the central axis. The radial distance from the central axisto the strain gauge Rc and the radial distance from the central axisto the strain gauge Rd are substantially the same.

The two strain gauges Ra and Rc and the two strain gauges Rb and Rd are arranged concentrically and line-symmetrically.

5 FIG. 1 1 As illustrated in, each of the strain gauges Ra, Rb, Rc, and Rd has a pattern circumferentially extending while being bent in a zigzag manner. Each of the strain gauges Ra, Rb, Rc, and Rd has a plurality of resistance lines rcircumferentially arrayed and substantially parallel to one another. Each of the resistance lines rextends in a direction having both radial and circumferential components.

1 1 1 1 1 The resistance lines rof the strain gauges Ra and Rd are inclined to a circumferential one side with respect to the radial direction. The resistance lines rof the strain gauges Rb and Rc are inclined to the circumferential other side with respect to the radial direction. The inclination angle of the resistance line rwith respect to the radial direction is, for example, 45°. The end parts of the resistance lines rcircumferentially adjacent to each other are alternately connected radially inside or radially outside. Due to this, the plurality of resistance lines rare connected in series as a whole.

62 9 9 9 The second torque sensorincludes four strain gauges Re, Rf, Rg, and Rh. Among the four strain gauges Re, Rf, Rg, and Rh, the two strain gauges Re and Rf are arranged at intervals in the circumferential direction. The two strain gauges Re and Rf are each provided in a semicircular arc shape in a range of about 180° centered on the central axis. The radial distance from the central axisto the strain gauge Re and the radial distance from the central axisto the strain gauge Rf are substantially the same.

9 9 9 Among the four strain gauges Re, Rf, Rg, and Rh, the other two strain gauges Rg and Rh are disposed radially outside relative to the two strain gauges Re and Rf. The two strain gauges Rg and Rh are arranged at intervals in the circumferential direction. The two strain gauges Rg and Rh are each provided in a semicircular arc shape in a range of about 180° centered on the central axis. The radial distance from the central axisto the strain gauge Rg and the radial distance from the central axisto the strain gauge Rh are substantially the same.

The two strain gauges Re and Rg and the two strain gauges Rf and Rh are arranged concentrically and line-symmetrically.

5 FIG. 2 2 As illustrated in, each of the strain gauges Re, Rf, Rg, and Rh has a pattern circumferentially extending while being bent in a zigzag manner. Each of the strain gauges Re, Rf, Rg, and Rh has a plurality of resistance lines rcircumferentially arrayed and substantially parallel to one another. Each of the resistance lines rextends in a direction having both radial and circumferential components.

2 2 2 2 2 The resistance lines rof the strain gauges Re and Rh are inclined to a circumferential one side with respect to the radial direction. The resistance lines rof the strain gauges Rf and Rg are inclined to the circumferential other side with respect to the radial direction. The inclination angle of the resistance line rwith respect to the radial direction is, for example, 45°. The end parts of the resistance lines rcircumferentially adjacent to each other are alternately connected radially inside or radially outside. Due to this, the plurality of resistance lines rare connected in series as a whole.

6 FIG. 6 FIG. 1 61 1 is a circuit diagram of a first bridge circuit Cincluding the four strain gauges Ra, Rb, Rc, and Rd of the first torque sensor. As illustrated in, the four strain gauges Ra, Rb, Rc, and Rd are connected to each other to form the first bridge circuit C.

1 11 12 The strain gauge Ra and the strain gauge Rb are connected in series in this order. The strain gauge Rc and the strain gauge Rd are connected in series in this order. Between the positive pole and the negative pole of the power supply voltage, the rows of the two strain gauges Ra and Rb and the rows of the two strain gauges Rc and Rd are connected in parallel. A first voltmeter Vis connected between a midpoint Mof the two strain gauges Ra and Rb and a midpoint Mof the two strain gauges Rc and Rd.

1 1 33 9 1 1 33 9 1 1 The resistance value of each of the resistance lines rchanges in accordance with the torque applied to the region where the resistance line ris disposed. For example, when the diaphragmis applied with torque directed toward a circumferential one side about the central axis, the resistance value of each resistance line rof the two strain gauges Ra and Rd decreases, and the resistance value of each resistance line rof the other two strain gauges Rb and Rc increases. For example, when the diaphragmis applied with torque directed toward the circumferential other side about the central axis, the resistance value of each resistance line rof the two strain gauges Ra and Rd increases, and the resistance value of each resistance line rof the other two strain gauges Rb and Rc decreases. In this manner, the two strain gauges Ra and Rd and the other two strain gauges Rb and Rc exhibit resistance value changes in orientations opposite to each other with respect to the torque.

11 12 1 52 33 1 When the resistance values of the four strain gauges Ra, Rb, Rc, and Rd change, the potential difference between the midpoint Mof the two strain gauges Ra and Rb and the midpoint Mof the two strain gauges Rc and Rd changes, and therefore the output value of the first voltmeter Valso changes. The circuitdetects the orientation and magnitude of the torque applied to the diaphragmbased on the output value of this first voltmeter V.

7 FIG. 7 FIG. 2 62 2 is a circuit diagram of a second bridge circuit Cincluding the four strain gauges Re, Rf, Rg, and Rh of the second torque sensor. As illustrated in, the four strain gauges Re, Rf, Rg, and Rh are connected to each other to form the second bridge circuit C.

2 21 22 The strain gauge Re and the strain gauge Rf are connected in series in this order. The strain gauge Rg and the strain gauge Rh are connected in series in this order. Between the positive pole and the negative pole of the power supply voltage, the rows of the two strain gauges Re and Rf and the rows of the two strain gauges Rg and Rh are connected in parallel. A second voltmeter Vis connected between a midpoint Mbetween the two strain gauges Re and Rf and a midpoint Mbetween the two strain gauges Rg and Rh.

2 2 33 9 2 2 33 9 2 2 The resistance value of each of the resistance lines rchanges in accordance with the torque applied to the region where the resistance line ris disposed. For example, when the diaphragmis applied with torque directed toward a circumferential one side about the central axis, the resistance value of each resistance line rof the two strain gauges Re and Rh decreases, and the resistance value of each resistance line rof the other two strain gauges Rf and Rg increases. For example, when the diaphragmis applied with torque directed toward the circumferential other side about the central axis, the resistance value of each resistance line rof the two strain gauges Re and Rh increases, and the resistance value of each resistance line rof the other two strain gauges Rf and Rg decreases. In this manner, the two strain gauges Re and Rh and the other two strain gauges Rf and Rg exhibit resistance value changes in orientations opposite to each other with respect to the torque.

21 22 2 52 33 2 When the resistance values of the four strain gauges Re, Rf, Rg, and Rh change, the potential difference between the midpoint Mof the two strain gauges Re and Rf and the midpoint Mof the two strain gauges Rg and Rh changes, and therefore the output value of the second voltmeter Valso changes. The circuitdetects the orientation and magnitude of the torque applied to the diaphragmbased on the output value of this second voltmeter V.

1 61 62 52 61 62 60 61 62 The wave reducerof the present example embodiment includes the two torque sensorsand. The circuituses any one of the output signals of the two torque sensorsandas the output signal of the torque sensor. With the two torque sensorsand, even when an abnormality occurs in any one of the torque sensors, the torque can be detected by the other torque sensor. When an abnormality occurs in any one of the torque sensors, the abnormality can be detected.

70 1 70 41 70 5 FIG. The angle sensoris a sensor for detecting the rotation angle of a rotational motion input to the wave reducer. That is, the angle sensoris a sensor having an output value that is variable in accordance with the rotation angle of the cam. As illustrated in, the angle sensorincludes eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp. The eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp are arranged at intervals in the circumferential direction.

Each of the eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp is formed of one conductive wire. Each of the strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp has a resistance line extending in a circular arc shape along the circumferential direction. However, in each of the strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp, the resistance line extending in the circumferential direction may be repeatedly arranged in the radial direction. The resistance line of each of the strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp may extend in the radial direction. In each of the strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp, the resistance line extending in the radial direction may be repeatedly arranged in the circumferential direction.

3 3 3 31 32 8 FIG. 8 FIG. Among the eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp, the four strain gauges Ri, Rk, Rm, and Ro not adjacent to one another are connected to one another to form a third bridge circuit C.is a circuit diagram of the third bridge circuit C. As illustrated in, the strain gauge Ri and the strain gauge Rk are connected in series in this order. The strain gauge Ro and the strain gauge Rm are connected in series in this order. Between the positive pole and the negative pole of the power supply voltage, the rows of the two strain gauges Ri and Rk and the rows of the two strain gauges Ro and Rm are connected in parallel. A third voltmeter Vis connected between a midpoint Mbetween the two strain gauges Ri and Rk and a midpoint Mbetween the two strain gauges Ro and Rm.

4 4 4 41 42 9 FIG. 9 FIG. Among the eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp, the remaining four strain gauges Rj, Rl, Rn, and Rp are connected to one another to form a fourth bridge circuit C.is a circuit diagram of the fourth bridge circuit C. As illustrated in, the strain gauge Rp and the strain gauge Rn are connected in series in this order. The strain gauge Rj and the strain gauge Rl are connected in series in this order. Between the positive pole and the negative pole of the power supply voltage, the rows of the two strain gauges Rp and Rn and the rows of the two strain gauges Rj and Rl are connected in parallel. A fourth voltmeter Vis connected between a midpoint Mof the two strain gauges Rp and Rn and a midpoint Mof the two strain gauges Rj and Rl.

1 33 30 9 When the wave reduceris driven, a circumferentially extending part (hereinafter called an “extension part”) and a circumferentially contracting part (hereinafter called a “contraction part”) are generated in the diaphragmof the flex gear. Specifically, two extension parts and two contraction parts are alternately generated in the circumferential direction. That is, the extension part and the part are alternately generated at intervals of 90° in the circumferential direction about the central axis. Then, a location where the extension part and the contraction part are generated rotates at the first rotational speed described above.

33 The resistance value of each of the eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp changes in accordance with circumferential extension and contraction of the diaphragm. For example, when the extension part described above overlaps a certain strain gauge, the resistance value of the strain gauge increases. When the contraction part described above overlaps a certain strain gauge, the resistance value of the strain gauge decreases.

5 FIG. 3 In the example of, when the contraction part overlaps the strain gauges Ri and Rm, the extension part overlaps the strain gauges Rk and Ro. When the extension part overlaps the strain gauges Ri and Rm, the contraction part overlaps the strain gauges Rk and Ro. Therefore, in the third bridge circuit C, the strain gauges Ri and Rm and the strain gauges Rk and Ro exhibit resistance value changes in opposite orientations.

5 FIG. 4 In the example of, when the contraction part overlaps the strain gauges Rp and RI, the extension part overlaps the strain gauges Rn and Rj. When the extension part overlaps the strain gauges Rp and Rl, the contraction part overlaps the strain gauges Rn and Rj. Therefore, in the fourth bridge circuit C, the strain gauges Rp and Rl and the strain gauges Rn and Rj exhibit resistance value changes in opposite orientations.

70 3 4 As described above, the angle sensorincludes the two sets of bridge circuits Cand Cincluding the plurality of strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp.

10 FIG. 10 FIG. 10 FIG. 10 FIG. 3 3 3 4 4 4 1 3 4 3 4 3 4 is a graph showing temporal changes of an output value vof the third voltmeter Vof the third bridge circuit Cand an output value vof the fourth voltmeter Vof the fourth bridge circuit C. The horizontal axis of the graph ofrepresents time. The vertical axis of the graph ofrepresents a voltage value. When the wave reduceris driven, the output values vand vhaving a sinusoidal shape that periodically change are obtained from the third voltmeter Vand the fourth voltmeter V, respectively, as illustrated in. A cycle T of the output values vand vcorresponds to ½ times the cycle of the first rotation speed described above.

3 3 4 4 3 4 4 4 3 4 3 4 3 3 The output value vof the third voltmeter Vand the output value vof the fourth voltmeter Vhave a phase difference of about ¼ cycle. That is, the output values of the two sets of bridge circuits Cand Chave a phase difference of about ¼ cycle. Then, the orientation of the rotary motion that is input can be determined by whether the phase of the output value vof the fourth voltmeter Vis advanced by ⅛ cycles (¼ cycles of the output values vand v) of the first rotation speed or delayed by ⅛ cycles (¼ cycles of the output values vand v) of the first rotation speed with respect to the phase of the output value vof the third voltmeter V.

52 1 3 3 4 4 52 3 3 4 4 52 3 4 The circuitdetects the rotation angle of the rotational motion input to the wave reducerbased on the output value vof the third voltmeter Vand the output value vof the fourth voltmeter V. Specifically, the circuitstores a function table in which a combination of the output value vof the third voltmeter Vand the output value vof the fourth voltmeter Vis associated with the rotation angle. The circuitoutputs the rotation angle by inputting the output values vand vto the function table.

1 30 61 62 30 1 When the wave reduceris driven, cyclic flexural deformation occurs in the flex gear. Therefore, the output signal of the first torque sensorand the output signal of the second torque sensordescribed above include a component reflecting the torque originally desired to be measured and an error component (ripple error) caused by the periodic flexural deformation of the flex gear. The ripple error changes in a sinusoidal shape in accordance with the rotation angle of the rotational motion input to the wave reducer.

52 70 61 62 52 61 62 52 30 Then, the circuitcalculates the above-described ripple error in accordance with the rotation angle detected by the angle sensor. Thereafter, the output signals of the first torque sensorand the second torque sensorare corrected using the calculated ripple error. Specifically, the circuitincreases or decreases the output signals of the first torque sensorand the second torque sensorin a direction of canceling the ripple error. As a result, the circuitcan output, with higher accuracy, the torque applied to the flex gear.

52 61 62 3 4 3 4 52 Note that the circuitmay multiply and combine, with the output signals of the first torque sensorand the second torque sensor, the output values vand vof the third voltmeter Vand the fourth voltmeter V, respectively, by a predetermined coefficient without calculating the rotation angle described above. This reduces processing load on calculation of the rotation angle. Therefore, the calculation speed of the circuitcan be improved.

80 41 80 41 80 5 FIG. The thrust sensoris a sensor for detecting a thrust force applied to the cam. That is, the thrust sensoris a sensor having an output value that is variable in accordance with the thrust force applied to the cam. The thrust force is a force in the axial direction. As illustrated in, the thrust sensorincludes two outer strain gauges Rq and Rr and two inner strain gauges Rs and Rt. The two inner strain gauges Rs and Rt are disposed more radially inward than the two outer strain gauges Rq and Rr.

60 9 9 9 In the present example embodiment, the two outer strain gauges Rq and Rr are disposed radially outside the torque sensor. The two outer strain gauges Rq and Rr are arranged at intervals in the circumferential direction. The two outer strain gauges Rq and Rr are each provided in a semicircular arc shape in a range of about 180° centered on the central axis. The radial distance from the central axisto the outer strain gauge Rq and the radial distance from the central axisto the outer strain gauge Rr are substantially the same.

60 9 9 9 In the present example embodiment, the two inner strain gauges Rs and Rt are disposed radially inside the torque sensor. The two inner strain gauges Rs and Rt are arranged at intervals in the circumferential direction. The two inner strain gauges Rs and Rt are each provided in a semicircular arc shape in a range of about 180° centered on the central axis. The radial distance from the central axisto the inner strain gauge Rs and the radial distance from the central axisto the inner strain gauge Rt are substantially the same.

That is, the two outer strain gauges Rq and Rr and the two inner strain gauges Rs and Rt are arranged at intervals in the radial direction.

5 FIG. 3 3 9 30 3 3 As illustrated in, each of the outer strain gauges Rq and Rr and the inner strain gauges Rs and Rt has a pattern circumferentially extending while being bent in a zigzag manner. Each of the strain gauges Rq, Rr, Rs, and Rt has a plurality of resistance lines rcircumferentially arrayed and substantially parallel to one another. The resistance line reach extend in the radial direction about the central axisof the flex gear. The end parts of the resistance lines rcircumferentially adjacent to each other are alternately connected radially inside or radially outside. Due to this, the plurality of resistance lines rare connected in series as a whole.

11 FIG. 11 FIG. 5 80 5 is a circuit diagram of a fifth bridge circuit Cincluding the outer strain gauges Rq and Rr and the inner strain gauges Rs and Rt of the thrust sensor. As illustrated in, the two outer strain gauges Rq and Rr and the two inner strain gauges Rs and Rt are connected to each other to form the fifth bridge circuit C.

5 51 52 The strain gauge Rq and the strain gauge Rs are connected in series in this order. The strain gauge Rt and the strain gauge Rr are connected in series in this order. Between the positive pole and the negative pole of the power supply voltage, two rows of the strain gauges Rq and Rs and two rows of the strain gauges Rt and Rr are connected in parallel. A fifth voltmeter Vis connected between a midpoint Mof the two strain gauges Rq and Rs and a midpoint Mof the two strain gauges Rt and Rr.

3 80 33 30 All of the plurality of resistance lines rincluded in the four strain gauges Rq, Rr, Rs, and Rt of the thrust sensorextend in the radial direction. For this reason, the change in the resistance value of the strain gauges Rq, Rr, Rs, and Rt due to the circumferential torque is extremely small. However, when the diaphragmof the flex gearis displaced in the axial direction, the resistance values of the strain gauges Rq, Rr, Rs, and Rt change.

33 20 33 20 33 Specifically, when the radial inner end part of the diaphragmis displaced in a direction getting close to the internal gear, of the four strain gauges Rq, Rr, Rs, and Rt, the resistance values of the two outer strain gauges Rq and Rr increase, and the resistance values of the two inner strain gauges Rs and Rt decrease. On the other hand, when the radial inner end part of the diaphragmis displaced in a direction away from the internal gear, of the four strain gauges Rq, Rr, Rs, and Rt, the resistance values of the two outer strain gauges Rq and Rr decrease, and the resistance values of the two inner strain gauges Rs and Rt increase. In this manner, the two outer strain gauges Rq and Rr and the two inner strain gauges Rs and Rt exhibit resistance value changes in orientations opposite to each other with respect to the axial displacement of the diaphragm.

51 52 5 52 30 5 When the resistance values of the four strain gauges Rq, Rr, Rs, and Rt change, the potential difference between the midpoint Mof the two strain gauges Rq and Rs and the midpoint Mof the two strain gauges Rt and Rr changes, and therefore the output value of the fifth voltmeter Valso changes. The circuitdetects the orientation and magnitude of the thrust force applied to the flex gearbased on the output value of this fifth voltmeter V.

70 3 4 3 4 3 4 3 4 1 103 1 102 3 4 3 4 41 As described above, the angle sensorincludes the two sets of bridge circuits Cand C. The output values vand vof the bridge circuits Cand Chave a sinusoidal shape and have a phase difference of about ¼ cycle from each other. The amplitudes of the output values vand vare substantially constant. However, when a force acts from the input side of the wave reduceras at the time of acceleration of the motor, or when an external force acts from the output side of the wave reducerdue to the inertial force of the armor the like, the amplitudes of the output values vand vof the two sets of bridge circuits Cand Cslightly changes due to the thrust force applied to the cam.

1 3 4 3 4 1 3 4 3 4 Specifically, when the force acts from the input side of the wave reducer, the amplitudes of the output values vand vof the two sets of bridge circuits Cand Cslightly decrease. When the force acts from the output side of the wave reducer, the amplitudes of the output values vand vof the two sets of bridge circuits Cand Cslightly increase.

52 70 80 52 3 4 3 4 52 3 4 3 4 70 41 41 3 4 70 Therefore, the circuitcorrects the output value of the angle sensorbased on the output value of the thrust sensor. Specifically, the circuitcorrects the output values vand vof the two sets of bridge circuits Cand C, respectively. More specifically, the circuitincreases or decreases the output values vand vof the two sets of bridge circuits Cand Cin a direction of canceling the influence of the thrust force. This can suppress the output value of the angle sensorfrom changing due to the thrust force applied to the cam. Therefore, the rotation angle of the camcan be accurately detected by the corrected output values vand vof the angle sensor.

52 60 3 4 70 80 52 3 4 70 60 30 The circuitcorrects the output value of the torque sensorbased on the output values vand vof the angle sensorafter corrected based on the output value of the thrust sensor. Specifically, the circuitcalculates the above-described ripple error based on the corrected output values vand vof the angle sensor, and corrects the output value of the torque sensorso as to cancel the ripple error. Due to this, the torque applied to the flex gearcan be detected more accurately.

70 80 Next, a method of correcting the output value of the angle sensorcaused by the thrust force without using the output value of the thrust sensorwill be described.

3 4 3 4 70 3 2 4 2 3 4 1 3 4 41 3 2 4 2 3 4 The output values vand vof the two sets of bridge circuits Cand Cof the angle sensorhave a relationship of a sine wave and a cosine wave. Therefore, the sum v{circumflex over ( )}+v{circumflex over ( )}of the squares of the output values vand vis always a constant value in an ideal state. However, when a force acts from the input side or the output side of the wave reducer, an error occurs in the amplitudes of the output values vand vdue to the thrust force applied to the cam, and therefore the sum v{circumflex over ( )}+v{circumflex over ( )}of the squares of the output values vand vdeviates from a constant value.

52 3 4 3 4 3 2 4 2 3 4 3 4 52 3 4 4 3 2 4 2 3 4 3 4 3 4 41 1 41 3 4 70 Therefore, the circuitcorrects the output values vand vof the two sets of bridge circuits Cand Cso as to bring the sum v{circumflex over ( )}+v{circumflex over ( )}of the squares of the output values vand vof the two sets of bridge circuits Cand Cclose to a constant value. For example, the circuitnormalizes the output values vand vso that the sum vv{circumflex over ( )}+v{circumflex over ( )}of the squares of the output values vand vis always a constant value. This can suppress the output values vand vof the bridge circuits Cand Cfrom changing due to the thrust force applied to the cameven when a force acts from the input side or the output side of the wave reducer. Therefore, the rotation angle of the camcan be accurately detected by the corrected output values vand vof the angle sensor.

52 60 3 4 70 52 3 4 70 60 30 The circuitcorrects the output value of the torque sensorbased on the output values vand vof the angle sensorafter corrected based on the normalization described above. Specifically, the circuitcalculates the above-described ripple error based on the corrected output values vand vof the angle sensor, and corrects the output value of the torque sensorso as to cancel the ripple error. Due to this, the torque applied to the flex gearcan be detected more accurately.

52 3 4 41 The circuitmay output the correction amounts of the output values vand vby the normalization as a detection value representing the thrust force applied to the cam.

52 3 4 3 4 3 4 70 100 3 4 70 100 70 The circuitmay output an alert signal when the sum of the squares of the output values vand vof the two sets of bridge circuits Cand Cis out of a predetermined range. The alert signal is a signal indicating that there is a possibility that at least one of the output values vand vof the angle sensoris not normal. This enables a control unit or the user of the industrial machineto recognize that there is a possibility that at least one of the output values vand vof the angle sensoris not normal based on the alert signal. Therefore, it is possible to stop the operation of the industrial machineand take measures such as inspection of the angle sensor.

Although the example embodiments of the present disclosure have been described above, the present disclosure is not limited to the above example embodiments. Hereinafter, various modifications will be described focusing on differences from the example embodiment described above.

1 52 70 52 1 1 52 In the above example embodiments, the wave reducerincludes the circuitfor correcting the output value of the angle sensor. However, the circuitmay be provided outside the wave reducer. That is, the wave reducerand the circuitmay constitute a drive system.

70 80 1 52 1 52 70 80 In this case, the angle sensorand the thrust sensorof the wave reducermay be electrically connected to the circuitprovided outside the wave reducer, and the circuitmay correct the output value of the angle sensorbased on the output value of the thrust sensor.

70 1 52 1 52 3 4 3 4 3 2 4 2 3 4 3 4 70 Alternatively, the angle sensorof the wave reducerand the circuitprovided outside the wave reducermay be electrically connected, and the circuitmay correct the output values vand vof the two sets of bridge circuits Cand Cso as to bring the sum v{circumflex over ( )}+v{circumflex over ( )}of the squares of the output values vand vof the two sets of bridge circuits Cand Cof the angle sensorclose to a constant value.

52 70 1 One circuitmay correct the output values of the angle sensorsof a plurality of the wave reducers.

60 61 62 60 61 62 In the above example embodiment, the torque sensorincludes the first torque sensorand the second torque sensor. However, the torque sensormay be only any one of the first torque sensorand the second torque sensor.

80 5 80 5 5 5 5 In the above example embodiments, the thrust sensorincludes only one set of the fifth bridge circuit Cincluding the outer strain gauges Rq and Rr and the inner strain gauges Rs and Rt. However, the thrust sensormay include two sets of the fifth bridge circuits Ceach including the outer strain gauges Rq and Rr and the inner strain gauges Rs and Rt. By doing this, even when an abnormality occurs in any one of the fifth bridge circuits C, the thrust force can be detected by the other of the fifth bridge circuits C. When an abnormality occurs in any one of the fifth bridge circuits C, the abnormality can be detected.

1 30 101 20 20 101 30 In the wave reducerof the above example embodiments, the flex gearis fixed to the base frame, and the internal gearrotates at the second rotational speed after deceleration. However, the internal gearmay be fixed to the base frame, and the flex gearmay rotate at the second rotational speed after deceleration.

30 33 31 30 33 31 The flex gearof the above example embodiment is a so-called “hat type” gear in which the diaphragmexpands radially outward from the body. However, the flex gearmay be a so-called “cup type” gear in which the diaphragmexpands radially inward from the body.

100 100 In the above example embodiments, the industrial machineis an industrial robot having an arm. However, the industrial machinemay be another device such as an assist suit or an unmanned transport vehicle.

In addition, detailed configurations of the wave reducer, the industrial machine, and the drive system may be appropriately changed without departing from the gist of the present disclosure. The elements appearing in the above example embodiment and modifications may be appropriately combined as long as no contradiction occurs.

The present technology can have the following configurations.

(1) A wave reducer including: a cam having a non-circular outer surface; a flex gear flexurally deformed by rotation of the cam; an internal gear meshing with the flex gear; an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam; a thrust sensor located in the flex gear and having an output value that is variable in accordance with a thrust force applied to the cam; and a circuit electrically connected to the angle sensor and the thrust sensor, wherein the circuit corrects an output value of the angle sensor based on an output value of the thrust sensor.

(2) The wave reducer according to (1), wherein the angle sensor includes two sets of bridge circuits including a plurality of strain gauges, output values of the two sets of bridge circuits have a phase difference of about ¼ cycle, and the circuit corrects output values of the two sets of bridge circuits.

(3) The wave reducer according to (1) or (2) further including a torque sensor having an output value that is variable in accordance with torque applied to the flex gear, wherein the circuit corrects an output value of the torque sensor based on an output value of the angle sensor after corrected based on an output value of the thrust sensor.

(4) The wave reducer according to any one of (1) to (3), wherein the thrust sensor includes a bridge circuit including an outer strain gauge having a resistance line extending in a radial direction about a central axis of the flex gear; and an inner strain gauge having a resistance line extending in a radial direction about the central axis of the flex gear and disposed more radially inward than the outer strain gauge.

(5) An industrial machine including the wave reducer according to any one of (1) to (4).

(6) A drive system including a wave reducer and a circuit, wherein the wave reducer includes a cam having a non-circular outer surface, a flex gear flexurally deformed by rotation of the cam, an internal gear meshing with the flex gear, an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam, and a thrust sensor located in the flex gear and having an output value that is variable in accordance with a thrust force applied to the cam, and the circuit corrects an output value of the angle sensor based on an output value of the thrust sensor.

(7) A correction method of correcting an output value of an angle sensor in a wave reducer including a cam having a non-circular outer surface, a flex gear flexurally deformed by rotation of the cam, an internal gear meshing with the flex gear, the angle sensor located in the flex gear, the angle sensor having an output value that is variable in accordance with a rotation angle of the cam, and a thrust sensor located in the flex gear and having an output value that is variable in accordance with a thrust force applied to the cam, the correction method including correcting the output value of the angle sensor based on an output value of the thrust sensor.

(8) A wave reducer including: a cam having a non-circular outer surface; a flex gear flexurally deformed by rotation of the cam; an internal gear meshing with the flex gear; an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam; and a circuit electrically connected to the angle sensor, wherein the angle sensor includes two sets of bridge circuits including a plurality of strain gauges, output values of the two sets of bridge circuits have a phase difference of about ¼ cycle, and the circuit corrects output values of the two sets of bridge circuits so as to bring a sum of squares of the output values of the two sets of bridge circuits close to a constant value.

(9) The wave reducer according to (8), wherein the circuit outputs a correction amount of an output value of the bridge circuit as a detection value representing a thrust force applied to the cam.

(10) The wave reducer according to (8) or (9), wherein the circuit outputs an alert signal when a sum of squares of output values of the two sets of bridge circuits is out of a predetermined range.

(11) A drive system including a wave reducer and a circuit, wherein the wave reducer includes a cam having a non-circular outer surface, a flex gear flexurally deformed by rotation of the cam, an internal gear meshing with the flex gear, and an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam, and the angle sensor includes two sets of bridge circuits including a plurality of strain gauges, output values of the two sets of bridge circuits have a phase difference of about ¼ cycle, and the circuit corrects output values of the two sets of bridge circuits so as to bring a sum of squares of the output values of the two sets of bridge circuits close to a constant value.

(12) A correction method of correcting an output value of an angle sensor in a wave reducer including a cam having a non-circular outer surface, a flex gear flexurally deformed by rotation of the cam, an internal gear meshing with the flex gear, and an angle sensor located in the flex gear and having an output value that is variable in accordance with a rotation angle of the cam, wherein the angle sensor includes two sets of bridge circuits including a plurality of strain gauges, output values of the two sets of bridge circuits have a phase difference of about ¼ cycle, and the circuit corrects output values of the two sets of bridge circuits so as to bring a sum of squares of the output values of the two sets of bridge circuits close to a constant value.

The present disclosure can be used for, for example, a wave reducer, an industrial machine, a drive system, and a correction method.

Features of the above-described example embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.

While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.